As in the past, the purpose of this investigation will continue to be the identification and characterization of the entities elaborated by the intramitochondrial system of gene expression with regard to their specification, biosynthesis, function and regulation and attempts at detailed definition of their role in mitochondriogenesis and of their interaction with the extramitochondrial system in this process, in vivo and in vitro. Specifically we propose to perform: 1) An analysis in depth of the region of the mitochondrial genome responsible for the specification of apocytochrome B, of its expression and of regulatory effects exerted on and by it and its products. 2) A structural and functional analysis of mutationally altered cytochrome B molecules. 3) A continued search for novel, defined but pleiotropic mitochondrial phenotypes, their site of specification, and their function. 4) Attempts at performing mitochondrial fusion, complementation and recombination in vitro.